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Updated: Jun 20, 2026
High-throughput Assay to Phenotype Salmonella enterica Typhimurium Association, Invasion, and Replication in Macrophages
Published on: August 11, 2014
Comparative proteomic analysis of the PhoP regulon in Salmonella enterica serovar Typhi versus Typhimurium
Richelle C Charles1, Jason B Harris, Michael R Chase
1Division of Infectious Diseases, Massachusetts General Hospital, Boston, Massachusetts, USA. rccharles@partners.org
Background:
S. Typhi, a human-restricted Salmonella enterica serovar, causes a systemic intracellular infection in humans (typhoid fever). In comparison, S. Typhimurium causes gastroenteritis in humans, but causes a systemic typhoidal illness in mice. The PhoP regulon is a well studied two component (PhoP/Q) coordinately regulated network of genes whose expression is required for intracellular survival of S. enterica.
Methodology/Principal Findings:
Using high performance liquid chromatography mass spectrometry (HPLC-MS/MS), we examined the protein expression profiles of three sequenced S. enterica strains: S. Typhimurium LT2, S. Typhi CT18, and S. Typhi Ty2 in PhoP-inducing and non-inducing conditions in vitro and compared these results to profiles of phoP(-)/Q(-) mutants derived from S. Typhimurium LT2 and S. Typhi Ty2. Our analysis identified 53 proteins in S. Typhimurium LT2 and 56 proteins in S. Typhi that were regulated in a PhoP-dependent manner. As expected, many proteins identified in S. Typhi demonstrated concordant differential expression with a homologous protein in S. Typhimurium. However, three proteins (HlyE, STY1499, and CdtB) had no homolog in S. Typhimurium. HlyE is a pore-forming toxin. STY1499 encodes a stably expressed protein of unknown function transcribed in the same operon as HlyE. CdtB is a cytolethal distending toxin associated with DNA damage, cell cycle arrest, and cellular distension. Gene expression studies confirmed up-regulation of mRNA of HlyE, STY1499, and CdtB in S. Typhi in PhoP-inducing conditions.
Conclusions/Significance:
This study is the first protein expression study of the PhoP virulence associated regulon using strains of Salmonella mutant in PhoP, has identified three Typhi-unique proteins (CdtB, HlyE and STY1499) that are not present in the genome of the wide host-range Typhimurium, and includes the first protein expression profiling of a live attenuated bacterial vaccine studied in humans (Ty800).
Insights
This study identified three unique Salmonella Typhi proteins (CdtB, HlyE, STY1499) absent in S. Typhimurium, regulated by the PhoP system. These findings advance understanding of Salmonella virulence and host adaptation.
Area of Science:
- Microbiology
- Genomics
- Proteomics
Background:
- Salmonella enterica serovar Typhi (S. Typhi) causes typhoid fever, a systemic infection in humans.
- Salmonella enterica serovar Typhimurium (S. Typhimurium) causes gastroenteritis in humans but typhoidal illness in mice.
- The PhoP/Q regulon is crucial for intracellular survival of S. enterica serovars.
Purpose of the Study:
- To investigate protein expression profiles of S. Typhi and S. Typhimurium under PhoP-inducing and non-inducing conditions.
- To identify proteins regulated by the PhoP system in S. Typhi and S. Typhimurium.
- To compare PhoP-regulated proteins between S. Typhi and S. Typhimurium, focusing on Typhi-unique proteins.
Main Methods:
- Utilized high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) to analyze protein expression.
- Compared protein profiles of S. Typhimurium LT2, S. Typhi CT18, and S. Typhi Ty2 with their respective phoP/Q mutants.
- Examined protein expression under both PhoP-inducing and non-inducing conditions in vitro.
- Confirmed mRNA up-regulation for identified unique proteins using gene expression studies.
Main Results:
- Identified 53 PhoP-regulated proteins in S. Typhimurium LT2 and 56 in S. Typhi.
- Discovered three proteins (HlyE, STY1499, CdtB) in S. Typhi that lack homologs in S. Typhimurium.
- HlyE is a pore-forming toxin, STY1499 is of unknown function, and CdtB is a cytolethal distending toxin.
- Confirmed increased mRNA levels for HlyE, STY1499, and CdtB in S. Typhi under PhoP-inducing conditions.
Conclusions:
- This is the first protein expression study of the PhoP regulon using Salmonella mutants in PhoP.
- Identified three S. Typhi-unique proteins (CdtB, HlyE, STY1499) not found in S. Typhimurium.
- Provides insights into Salmonella virulence mechanisms and host-specific adaptations.
- Includes the first protein expression profiling of a live attenuated Salmonella vaccine (Ty800).
